Docs: Enhance README files with beginner-friendly guides (4 languages)

**Configuration Improvements:**
- Add comprehensive "Get AI API Keys" section (DeepSeek + Qwen)
- Split configuration into Beginner Mode and Expert Mode
- Add step-by-step setup guides with placeholder tables
- Add configuration checklist and field explanations
- Document smart default behavior for use_default_coins (v2.0.2)

**Startup/Monitoring Guides:**
- Add detailed 2-step system startup instructions
- Include expected output and error troubleshooting tables
- Add monitoring and graceful shutdown procedures
- Provide health check commands

**AI Decision Flow Updates:**
- Enhance flow diagram with emojis and wider boxes
- Add v2.0.2 improvement markers throughout
- Document position duration tracking
- Document accurate USDT PnL calculation with leverage
- Document enhanced AI freedom for raw data analysis
- Document improved position tracking (symbol_side keys)
- Add "Key Improvements in v2.0.2" summary section

**Code Changes:**
- Simplify config.json.example to beginner-friendly single trader
- Implement smart default: use_default_coins auto-enables when omitted
- Set default to true if false without coin_pool_api_url

**Files Updated:**
- README.md (English): +559 lines
- README.zh-CN.md (Chinese): +527 lines
- README.ru.md (Russian): +634 lines
- README.uk.md (Ukrainian): +521 lines
- config.json.example: Simplified configuration
- config/config.go: Smart default logic

Total: 2068+ additions across all documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

config/config.go

@@ -44,6 +44,11 @@ func LoadConfig(filename string) (*Config, error) {
 		return nil, fmt.Errorf("解析配置文件失败: %w", err)
 	}
 
+	// 设置默认值：如果use_default_coins未设置（为false）且没有配置coin_pool_api_url，则默认使用默认币种列表
+	if !config.UseDefaultCoins && config.CoinPoolAPIURL == "" {
+		config.UseDefaultCoins = true
+	}
+
 	// 验证配置
 	if err := config.Validate(); err != nil {
 		return nil, fmt.Errorf("配置验证失败: %w", err)